This invention relates to a multi-stand hot strip rolling mill.
During the hot rolling of metal strip, particularly steel strip, in a multi-stand rolling mill, the rolling may introduce defects into the strip so that the resultant strip, instead of being flat, has wavy edges or similar defects. Strip having such defects is unacceptable to many users and consequently it is necessary to make sure that the hot rolled strip is, as far as possible, free from these defects.
It has become a common practice in multi-stand cold strip rolling mills to provide a shapemeter for measuring strip shape immediately after the last stand of the mill. The strip is held under tension between the last stand and the coiler and the shapemeter engages the strip across its width so that the strip is deflected slightly and the shapemeter measures the components of strip tension across the width of the strip. The shape of the strip when free from tension can be deduced from the measured tension distribution, for example, if the tension distribution is uniform then the strip will be essentially flat when the tension is released. On the other hand, if the tension distribution across the width of the strip is not uniform then the strip will not be flat when the tension is released. Shape signals from the shapemeter are used to automatically adjust various control features on one or more stands of the mill so as to substantially eliminate the shape errors and so produce flat strip.
In British Patent Specification No. 1564389 there is disclosed a shapemeter for determining the degree of flatness of a metal strip during hot rolling thereof. The specification discloses that the metal strip being rolled passes over a plurality of individual sensing rollers arranged substantially side by side across the path taken by the strip. There is no disclosure in the specification as to exactly where the apparatus is positioned when the strip is being rolled in a multi-stand rolling mill. From a practical consideration it is believed that the apparatus is positioned between a pair of adjacent stands of the multi-stand rolling mill.
If the apparatus is positioned between the last two stands of the multi-stand rolling mill then any defects introduced into the strip at the last stand are not detected by the apparatus. One of the problems with a hot strip rolling mill is that there is a considerable distance between the last stand of the hot mill and the coiler in order to accomodate means for water cooling of the strip and this distance may be in the excess of 100 meters. For this reason if it is proposed to place a shapemeter roll downstream of, but close to the last stand of the hot mill, the shapemeter will not become effective until strip has been taken up by the coiler and tension has been developed in the strip. Consequently 100 meters or more of the strip is wasted before the control system operated by the shapemeter becomes operative.